Receiving a mental health diagnosis can be pivotal for service users, and it has been described in both positive and negative terms. What influences service-user experience of the diagnostic process is unclear; consequently, clinicians report uncertainty regarding best practice. This Review aims to understand and inform diagnostic practice through a comprehensive synthesis of qualitative data on views and experiences from key stakeholders (service users, clinicians, carers, and family). We searched five databases and identified 78 papers for inclusion, originating from 13 countries and including 2228 participants. Eligible papers were assessed for quality, and data were coded and then developed into themes, which generated a model representing factors to consider for clinicians conveying, and individuals receiving, mental health diagnoses. Themes included disclosure, information provision, collaboration, timing, stigma, and functional value of diagnosis for recovery. Variations between different stakeholders and clinical contexts are explored. Findings support an individualised, collaborative, and holistic approach to mental health diagnosis.